There comes a time in every teenager's life when they start to reject the things that elder siblings, and indeed parents, are into and begin to develop their own passions. And this is now starting to apply to youngsters in their choice of social networks and online platforms too.

For almost half a decade Twitter and Facebook have held a virtual monopoly on self-expression for both young and old as their members share images, links, videos and more with their circle of friends and acquaintances. The two pillars of social networking have also delivered an excellent platform for brands to engage with the type of audiences they like most too - young, influential, and even in these recessionary times, still able to access a fair share of disposable income.

There are however signs that a backlash against Twitter and, especially Facebook, is coming and that tomorrow's consumers might be ignoring the pair and creating their own new type of social networks.

Facebook - your parent's networkThere have been rumours for a while now that Facebook hasn't been quite so successful at attracting the young - you have to be 13 before you can legitimately have an account - and now a pair of high-profile articles have suggested that the social networking behemoth means very little to the next generation of teenagers.

Yesterday Mashable ran a feature written by 13 year old Ruby Karp who points out that whereas once Facebook was an obsession for her, now she is old enough to have an account none of her friends are using the service. She points to the fact that they perceive it as being a place for older people, and indeed expresses fears about what might happen if someone shares something inappropriate on Facebook which her parents might get to see.

Mashable also ran a follow up feature which suggested that Facebook might now start going the way of Yahoo. It points out that the search engine/portal still has more users in the US than Facebook, yet its lack of younger users makes it significantly less popular than its social network rival with advertisers.

The success of constrained mediaAt the same time influential blogger Andrew Chen wrote a story about what he calls ‘constrained media.' By this he means media that puts a limitation on the user whether it be the number of characters they can use in a post (Twitter) or the number of seconds a person can view an image before it disappears (SnapChat). He argues that these, alongside Instagram, have become hugely popular with the young as the limitations that are imposed make it very easy to create and share content. He hints that in the same way that Facebook and Twitter have marginalised blogging, constrained media formats might have the same impact on Facebook.

The other interesting element that Chen notes is that many of the new formats are much more about communication between individuals than sharing media across a network. He argues:

‘Discoverability of content is an important factor too. If you make it too easy to find the more effortful or highest skill content, this creates a kind of leaderboard that discourages content creation, although the content consumption experience might be improved. It's a tradeoff. SnapChat's private, ephemeral context means that it's the only place where it's safe to post crappy selfies of yourself.'

This begs the question where does this leave marketers who need to target the next generation? Well some brands have already begun tentatively experimenting with SnapChat (Taco Bell and Lynx) and Instagram (Topshop, Swarovski and others). However it is clear that while they have had limited success within that community the difference is that the campaigns are less viral and harder for users to discover. And they don't resonate at all on other platforms.

Facebook and Twitter have made things very easy for brands who want to share their content whether it was created specifically for that platform or just links to weightier content housed elsewhere.

The growth of constrained media, especially if it is at the expense of Facebook (and maybe even Twitter) could in the long run cause issues for brands, especially if they focus on younger consumers.

Facebook has a long way to fall, but we may remember 2012 as the year it finally peaked. It does however have massive purchasing power - it bought Instagram earlier this year primarily to connect with younger consumers - but if it needs to manage its new acquisitions very carefully.

Quickie guide to new social mediaSnapChat - Image exchange platform where users send pictures to each other which, once opened,can only be viewed for three seconds.

Instagram - Image sharing platform that is very popular among the young as it enables them to add filters to images which it can then share via the network. Now also offers Instagram video which enables users to create videos of a maximum time of 15 seconds. Twitter has a rival video service called Vine.

Ask FM - Social networking site where users can invite questions from other users on the site or from anonymous users. Has been in the news recently over accusations of cyber bullying by some of its users.

Dribbble - Image sharing site that limits its user to sharing images that are a maximum of 400×300 thumbnails.

Bebo - Yes the old site that AOL bought for a fortune has been acquired by its founder Michael Birch. It'll be fascinating to see if he can reinvent to attract a new generation of social networkers.